Estimating Debye Parameters from GPR Reflection Data Using Spectral Ratios

Abstract

In the GPR frequency range, electromagnetic wave attenuation is largely controlled by dielectric relaxation processes. A primary relaxation commonly occurs in the 10 -100 MHz range for many earth materials in which the GPR signal propagates effectively. This relaxation leads to strong nonlinearity in the frequency dependent attenuation and occurs in a frequency range that is often used for groundwater investigations.This non-linearity complicates data analysis but also may provide additional material property information. I investigate inversion for Debye relaxation parameters directly from GPR reflection data, including increasing the bandwidth of the signal by summing the response from 25 MHz, 50 MHz, 100 MHz, and 200 MHz radar antennas. I compute the timefrequency distribution using spectral decomposition, then use the method of spectral ratios to measure the attenuation vs frequency curve for significant reflection events. I then fit the curve with the multiparameter Debye model. Using synthetic and field data I show that this approach provides reliable estimates of the primary relaxation time for a variety of realistic subsurface models. This approach has the potential to improve our understanding of aquifer material properties.